1. Field of the Invention
The present invention relates to a thermostatic subcooling control valve. In particular, it relates to a thermostatic subcooling control valve which senses degree of supercooling (subcooling) of a refrigerant in a refrigerating cycle to control a flow rate of the refrigerant.
2. Description of the Prior Art
Heretofore, a thermostatic expansion valve has generally been used as a flow rate control valve of this type for a refrigerant in a refrigerating cycle. To carry out flow rate control of the refrigerant, heating degree of the evaporated refrigerant at an outlet of an evaporator is sensed by a temperature sensing element and, based on the sensing, the thermostatic expansion valve is operated.
The thermostatic expansion valve is designed, as described above, to have function of controlling the heating degree of the evaporated refrigerant at the outlet of the evaporator to within a predetermined temperature range. Accordingly, no matter how the heating degree of the refrigerant is controlled by the thermostatic expansion valve, it is impossible to attain increase in capability of the evaporator in the refrigerating cycle. In other words, the thermostatic expansion valve is designed to control the heating degree, and hence it has no function of enhancing capability in terms of improvement in refrigerating efficiency.
Further, the thermostatic expansion valve insufficient in terms of safety of the refrigerating cycle. Specifically, for example, even if pressure of the refrigerant in a high pressure-exposed portion in the refrigerating cycle becomes extraordinarily high to incur dangerous condition, the thermostatic expansion valve has no function of protecting an appliance disposed in a high pressure line in the refrigerating cycle from the extraordinarily high pressure because it is not so constructed as to operate based on the pressure in the high pressure-exposed portion in the refrigerating cycle.
To solve the above-described drawbacks of the thermostatic expansion valve, it has been proposed that a subcooling control valve is disposed downstream from a refrigerant condenser in a refrigerating cycle to control degree of supercooling (subcooling) of a high pressure refrigerant.
FIG. 3 shows one form of such a known subcooling control valve. The subcooling control valve 50 comprises a substantially cylindrical valve body 51 and a pressure responsive member 52 located on the top of the valve body 51. The pressure responsive member 52 is divided by a diaphragm 53 into an upper compartment 54 and a lower compartment 55. The valve body 51 comprises an upper valve chamber 56 and a lower valve chamber 57, and the upper valve chamber 56 and the lower valve chamber 57 are in communication with each other via a throttle 58 serving as a valve seat. The upper valve chamber 56 is unified with and in communication with the lower compartment 55 of the pressure responsive member 52.
The upper valve chamber 56 provided with a refrigerant inlet 59 in communication with a condenser, and the lower valve chamber 57 is provided with a refrigerant outlet 60 in communication with an evaporator. To the lower surface of the diaphragm 53, one end of a valve stem 61 is fixedly attached. To the other end of the valve stem 61, a valving element 62 is fixedly attached. The valving element 62 is suspended in the throttle 58, and a compression spring 63 is disposed under the valving element 62 to always bias the valving element 62 upward.
A refrigerant line 64 is located downstream from the refrigerant condenser and upstream to the refrigerant inlet 59 of the subcooling control valve 50, and thereon, a temperature sensing element 65 is placed in contact therewith for detecting a temperature of the refrigerant in the line 64. The temperature sensing element 65 is in communication with the upper compartment 54 of the pressure responsive member 52 via a capillary tube 66. The temperature sensing element 65, the capillary tube 66 and the upper compartment 54 are hermetically filled with a refrigerant, and change in the temperature of the refrigerant flowing in the line 64 in the refrigerating cycle is sensed by the temperature sensing element 65 to act on the diaphragm 53 of the pressure responsive member 52 as change in pressure.
Displacement of the valving element 62 of the subcooling control valve 50 relative to the throttle 58 is controlled according to balance of the pressure exerted on the diaphragm 53 by the upper compartment 54 of the pressure responsive member 52 via the capillary tube 66 on the basis of the temperature sensing by the temperature sensing element 65 versus the pressure in the line 64-the lower compartment 55 of the pressure responsive member 52 and the force of the compression spring 63 which are exerted on the diaphragm 53. According to the displacement of the valving element 62, opening degree of the throttle 58 is determined to thereby control flow rate of the refrigerant passing through the subcooling control valve 50.
In the conventional subcooling control valve 50 constructed as described above, however, it is required that the temperature sensing element 65 for sensing degree of supercooling of the refrigerant flowing downstream form the refrigerant condenser be provided separately from the valve body structure of the subcooling control valve 50 and that the capillary tube 66 be employed for communication between the temperature sensing element 65 and the subcooling control valve 50. Accordingly, in installation operation of the subcooling control valve 50 and the temperature sensing element 65 in the refrigerating cycle, it is inconvenient to place the subcooling control valve 50 and the temperature sensing element 65 at proper positions. In addition, there is undesired possibility of troubles such as breakage of the capillary tube 66 due to inaptitude in handling.
Further, the capillary tube 66 is made of a small-diameter tube and thus likely to undergo blockage during use for some reason to cause a situation where the subcooling control valve 50 is put out of action.
Moreover, the subcooling control valve 50 is so constructed that the temperature change of the refrigerant flowing downstream from the refrigerant condenser in the refrigerating cycle is sensed by means of the temperature sensing element 65 and the temperature change is exerted as pressure change of the refrigerant in the temperature sensing element 65 on the diaphragm 53 of the upper compartment 54 of the pressure responsive member 52 placed at a distance from the temperature sensing element 65 via the capillary tube 66. Accordingly, the subcooling control valve 50 has problems that delay is likely to occur in the response, and that since the temperature sensing element 65 is placed in contact with the refrigerant line 64 in the refrigerating cycle, it is difficult to precisely sense the temperature change of the refrigerant in the refrigerating cycle.
Furthermore, the lower compartment 55 of the pressure responsive member 52 exerts the pressure of the refrigerant in the lower compartment 55 on the diaphragm 53, whereas the upper compartment 54 transforms the temperature of the refrigerant in the line 64 located upstream to the lower compartment 55 into pressure and exerts the pressure on the diaphragm 53. In other words, the diaphragm 53 in the pressure responsive member 52 is operated not based on the temperature and pressure of the refrigerant at the same position but based on the temperatures and pressures of the refrigerant at the different positions in the course of flow. Accordingly, the subcooling control valve disadvantageously tends to have poor sensing and operating accuracy and thus to lack reliability.